The first example of dramatic irony occurs when Macbeth, on being invited to take his seat at the banquet table by Lennox, declares that 'The table's full.' At this point, he does not seem to have fully identified the one who is occupying his seat and when, once again, he is told that there is a place reserved for him, asks, 'Where?'
Lennox points at his seat and it is at this point that Macbeth recognizes the specter occupying his seat as Banquo's ghost. The others cannot see what he sees. He is visibly shaken, which provokes Lennox into asking what it is that is affecting him. Macbeth, who is now clearly upset by the appearance of Banquo's ghost, demands to know who it is that is playing a trick on him. The lords' reply is a clear indication that they do not know what he is talking about.
Macbeth then proceeds to address the ghost directly. The dramatic irony lies in the fact that only we, the audience, and Macbeth know that Banquo has been murdered and that his ghost is there to haunt his assassin (Macbeth). None of the others at the banquet table have any idea about Banquo's fate and believe him to be still alive.
Ross believes that his king is ill and asks the other lords to rise so that he might be excused. Lady Macbeth intervenes and asks them to sit. She explains that her husband is having a momentary fit and that if they react to his condition, it will worsen. She addresses him directly and questions his manliness. Macbeth replies that he is man enough to face any challenge, fit enough to face anything that might frighten even the devil.
Lady Macbeth accuses her husband of being a fearful coward who sees things which are not there, just as he had previously seen a nonexistent dagger. The dramatic irony finds emphasis in the fact that she, unlike her husband and the audience, cannot see the ghost.
When the ghost disappears, Macbeth regains some of his composure and goes to take his seat at the table. He then states, in part, the following:
...I drink to the general joy o' the whole table,
And to our dear friend Banquo, whom we miss;
Would he were here! to all, and him, we thirst,
And all to all.
It is dramatically ironic that he should drink a toast to Banquo, when he and the audience know that Banquo has been murdered, since one of the assassins he had hired to kill Banquo had reported on the success of their malicious venture. When Banquo's ghost reappears, Macbeth loses all civility and shouts at the spirit, commanding it to leave. The lords are obviously confused and concerned about their king's uncharacteristic behavior. Lady Macbeth, however, tries to set their minds at ease by explaining that Macbeth's condition is a customary affliction and that they should not be too concerned. This statement adds to the irony since the audience knows the real reason for Macbeth's reaction—the gory sight of Banquo's blood-drenched spirit.
Macbeth addresses the ghost once more and the lords, who do not know what he is about, can only stare and wonder at his craziness. When the ghost finally vanishes, Macbeth declares that he is a man again. Lady Macbeth intervenes and asks the gentlemen to leave, which they do. Macbeth then declares that it seems as if the ghost was there to have its revenge.
It will have blood; they say, blood will have blood: